1. Field of the Invention
The present invention generally relates to plasma processing technologies and, more specifically, to a method for monitoring process drift using characteristics of a plasma in a plasma processing system.
2. Description of the Related Art
Plasma enhanced semiconductor processing chambers are widely used in the manufacture of integrated devices. The process performance generally depends on the physical, chemical, and electrical properties of the plasma. For example, the uniformity and selectivity of a plasma etching process will be strongly related to the kinetic properties of energetic ions of the plasma at or near the surface of a processing substrate. In an anisotropic etch process, incident ions are made to strike a substrate surface with a narrow angular velocity distribution that is nearly perpendicular to the surface, thereby providing an ability to etch high aspect ratio features into the substrate. An ion velocity distribution that is substantially isotropic, however, may result in undesirable etching effects such as bowing or toeing of profile cavity sidewalls.
Furthermore, the kinetic energy distribution of plasma ions may also influence substrate processing result. Generally, a plasma contains chemically reactive species such as atomic radicals (Cl−), atomic ions (Cl+), molecular ions (Cl2+), and excited molecular (Cl2*), that are produced by electron-molecule collusions. Plasma generated during processing may have different concentration and/or ratios of atomic ions (Cl+) with respect to molecular ions (Cl2+). The dynamics of etching processes having different distribution density and/or mixture of atomic and molecular ions (Cl+, Cl2+) in the plasma may product different etch results.
Additionally, in plasma etching processes using fluorocarbon gases, released CFx and/or CFxHy from the plasma may redeposit on the sidewall of the etched surface in a process known as sidewall passivation. Sidewall passivation is utilized to control the sidewall profile during etching to enable a predetermined depth to be reached while maintaining a desired sidewall profile. However, as the component and/or ratios of the ions impacting the substrate surface are not controlled and/or known in conventional plasma processes, activated chemical reactions and material sputtered etched from the substrate surface may vary chamber to chamber and even process to process, thereby adversely impacting process control, repeatability and predictability of the etch processes.
We have determined that quantitative information about the properties, distribution and energy of ions in a plasma and other plasma characteristics will enable meaningful indications of the effectiveness of the process and quality of the process results, thereby enhancing process control, repeatability and predictability of the etch processes. We have also determined that the ability to provide plasma characteristics enables corresponding improvements in other plasma processes, such as plasma enhanced chemical vapor deposition, physical vapor deposition, plasma surface treatments, among other plasma processes.
Therefore, there is a need for methods for determining the effective ion energy and other plasma characteristics that can be used for improving plasma processes.